MAINTAINERS: aspeed: Update git tree URL

The description for joel/aspeed.git on git.kernel.org currently says:

    Old Aspeed tree. Please see joel/bmc.git

Let's update MAINTAINERS accordingly.

Signed-off-by: Zev Weiss <zev@bewilderbeest.net>
Acked-by: Joel Stanley <joel@jms.id.au>
Link: https://lore.kernel.org/r/20230922223405.24717-2-zev@bewilderbeest.net


Signed-off-by: Joel Stanley <joel@jms.id.au>